Doing ecology in new and exciting places sometimes means that perfect historical data aren’t readily available for comparison with the present, and more creative efforts might be in order. As part of my PhD dissertation with the Pringle Lab at Princeton University, I’ve been using recently declassified American government satellite imagery recorded high over Mozambique in 1977 to study how war-driven mammal declines in Gorongosa National Park might have affected tree cover in the park’s savannas.
The amount of tree cover is crucial in African savannas because many local species require relatively open, but not treeless habitats. Too many trees and you’ve got a forest, too few and it’s a grassland. Many of the mammal species nearly wiped out of Gorongosa in the early 1990s would have had strong effects on tree cover; some species, like elephants, topple and consume parts of trees, but others like wildebeest and zebra eat mostly grass, reducing fuel for fires that might otherwise burn up small trees. So it wasn’t immediately clear whether tree cover would have increased or decreased following the large-mammal declines, but a change in either direction would have major implications for Gorongosa’s savanna-adapted plants, birds, bugs, and other inhabitants.
I’m using the historical satellite imagery from 1977 alongside more recent commercial satellite photos from 2012 to measure the extent of tree cover throughout the park from before and after the mammal declines. I wrote briefly about the historical satellite image in 2013, but the more I’ve learned about the surveillance program that originally produced it, the more intrigued I’ve become.
The imagery comes from a series of spy satellites called Hexagon KH-9 that were built starting in the early 1960s at the height of the Cold War at the behest of the U.S. Central Intelligence Agency. The program’s existence was just declassified in 2011, but over 1,000 people worked in complete secrecy to construct the satellites.
The Hexagon satellites, only the second generation of American spy satellites, were an impressive feat of engineering, all the more so considering that they were designed largely before the age of computers, mainly with pencil, paper, and slide rule. The cameras had to focus on and photograph Earth from anywhere between 90 and 200 miles up, while they whizzed around in orbit. And, this was long before the days of digital photography, so enormous rolls of film (9 inches X about 20 miles!) were used. Perhaps the most James Bond-esque aspect of the program was how the film was returned to Earth. Re-entry capsules separated from the satellite, and parachuted downwards until they were low enough for an Air Force C-130 cargo plane to snag and retrieve in mid-air.
In learning all this, I’ve discovered that I very likely have a personal connection to this satellite program, too. My grandfather, Walter Daskin, was an aerospace engineer who specialized in re-entry systems, the very part of the Hexagon satellites built by the Philadelphia office of General Electric, where he worked during the time these satellites were designed. My first ventures into the world of science were building paper airplanes with my grandfather and conducting kitchen-counter experiments with my grandmother, a Ph.D. in chemistry. It’s hugely gratifying, yet almost unbelievably coincidental, to find that I’ve spent the last year studying Mozambican savanna using a spy satellite image that he may have played a part in acquiring so long ago.
For the U.S., the Hexagon program played a key role in providing American intelligence during the Cold War. Its high-resolution images allowed sensitive locations like foreign military bases and weapons systems to be photographed safely. For Gorongosa, I’ve found tree cover is about 30 percenthigher than it was in 1977. The most likely cause is the long-term decline in elephants and other browsing mammals, such as impala, reedbuck, eland, kudu, nyala, and bushbuck. The evidence to date suggests that other known determinants of savanna tree cover (rainfall and fire) are unlikely to explain this finding of increased tree cover.
If tree cover continues to expand in Gorongosa, the likelihood of full recovery for species like zebra, wildebeest and buffalo, which prefer open, grassy habitats might be somewhat diminished. But, that’s not too great a concern yet. There are still huge open areas in Gorongosa on the floodplain around Lake Urema at the park’s center. More likely is that certain areas once preferred by these species may not be the areas where they will recover first. It will be important to keep tracking tree cover in Gorongosa as the park’s herds recover. I think my grandfather would be proud to see how I’ve repurposed the results of his and so many others’ efforts for modern science and conservation.